The formation of hollow glass microspheres (HGMs) is well known in the art. The production of hollow glass microspheres has been described in U.S. Pat. No. 3,365,315 (Beck); U.S. Pat. No. 4,661,137 (Garnier); and U.S. Pat. No. 5,256,180 (Garnier), and which are incorporated herein by reference.
It is also known in the art to produce large macrospheres having hollow glass walls which provide a semipermeable liquid separation medium for containing absorbents. The production of macrosphere structures can be seen in reference to U.S. Pat. Nos. 5,397,759 and 5,225,123 to Torobin and which are incorporated herein by reference. The Torobin references disclose hollow glass macrospheres comprising multiple particle glass walls. The reference teaches the use of the macrospheres for gas/liquid separation and for use with absorbents but does not discuss any features or characteristics which would make the macrospheres suitable as a hydrogen storage medium.
U.S. Pat. No. 4,842,620 (PPG Industries) is directed to non-crystalline silica fibers having porous walls which are used in gas separation. The fibers described in this application have different physical characteristics than microspheres and which makes fibers less desirable with respect to hydrogen separation and storage capabilities.
U.S. Pat. No. 6,358,532 (CaP Biotechnology, Inc.) uses porous-wall hollow glass microspheres for cell clustering and biomedical uses. The porous-wall structures are designed to readily release microsphere contents when present within a biotic system. Alternatively, the microspheres are used to provide a substrate to support cell growth within the porous-wall structure.
While the above references disclose a variety of glass microspheres and porous-wall structures having various uses in material separation or drug delivery capabilities, there remains room for improvement and variation within the art.